Nicarbazin and the polyether antibiotics are known anticoccidials. However, certain strains of Eimeria, the causative organism of coccidiosis, exhibit or develop over time a resistance to certain of the anticoccidials. See "Chemotherapy of Chicken Coccidiosis," Advances in Pharmacology and Chemotherapy II, 221-293 (1973). The combinations of the present invention unexpectedly exhibit activity against strains which have reduced sensitivity to each compound when used individually. Furthermore, when employed alone at its accepted dose, nicarbazin causes some growth inhibition. See German Pat. No. 2,154,049. Therefore, it is desirable to reduce the dose of nicarbazin, if this can be achieved without reducing anticoccidial efficacy. The present combinations are also advantageous in that they permit the use of lower levels of nicarbazin.
Combinations of anticoccidials have previously been disclosed. Representative combinations include the following. U.S. Pat. Nos. 4,075,323 and 4,083,962, describe combinations of two polyether antibiotic anticoccidials. U.S. Pat. No. 4,061,755, is directed to the combination of monensin and metichlorpindol.
U.S. Pat. No. 3,761,594 describes the combination of meticlorpindol with 4-hydroxyquinolines. Nicarbazin has been combined with certain quanidine compounds (German Pat. No. 2,154,049). U.K. No. 1,463,519 describes the combination of purines with inter alia, monensin and nicarbazin.